Breyer's opinion in the death penalty case today is particularly bad. He agrees that the judge should not impose the death penalty, but he refuses to accept the argument of the others that the defendent has a 6A right to a jury trial. Instead, he hangs his opinion entirely on the 8A ("cruel and unusual"), and just gives a bunch of lame arguments against the death penalty!

He says in the opinion:

death is not reversible

potentially arbitrary application of the death penalty

death sentences almost five times more likely when victim is of a high socio-economic status

the suffering inherent in a prolonged wait for execution.

inadequacy of representation in capital cases, a fact that aggravates the other failings

other nations have increasingly abandoned capital punishment

only 3% of the Nation's counties account for 50% of the Nation's death sentences

Some of these arguments might persuade someone that the death penalty should be abolished, but do nothing for Breyer's legal argument. Eg, a judge could compensate for lousy lawyering better than a jury. Other nations don't even have a right to a jury trial. The prolonged wait is caused by judges like Breyer who don't believe in the death penalty anyway. And the last statistic is almost completely meaningless. It might also be true that 3% of the counties have 50% of the nation's murders. Much of US crime is concentrate in a few urban counties. It is a textbook example of lying with statistics because it is intended to show that the death penalty is applied inequitably in the US, but it actually doesn't show that at all.

Volokh's warblog has some additional statistics related to this point.